{"id":1867,"date":"2020-11-16T10:02:48","date_gmt":"2020-11-16T10:02:48","guid":{"rendered":"https:\/\/rentabilitet.dk\/opgaver\/?page_id=1867"},"modified":"2020-11-16T10:02:55","modified_gmt":"2020-11-16T10:02:55","slug":"class-diagram","status":"publish","type":"page","link":"https:\/\/rentabilitet.dk\/opgaver\/diverse-eksamensopgaver\/class-diagram\/","title":{"rendered":"Class diagram"},"content":{"rendered":"

Structure
\n<\/strong> After having established the classes in the system, the structure will now be defined with the
\nuse of a class diagram.<\/p>\n

Theory
\n<\/strong> The purpose of the class diagram is to describe structural relations between objects and classes
\nin a problem domain (Lars Mathiassen, 2000, p. 71). The structural relations are different for
\nthe classes and objects which will be described below.<\/p>\n

Class structures
\n<\/strong> The relations between the classes are abstract, static and general, and can consist of a
\ngeneralisation. A generalisation is a general class that describes the properties that are common
\nfor a group of subclasses. Generalisations can be expressed linguistically using the formulation
\n\u201cis-a\u201d. The subclasses inherits all of the properties and behaviors that the super-class contains
\n(Lars Mathiassen, 2000, p. 75). A class is abstract if it has no related objects. These classes are
\nused for descriptive reasons and the class names are written in italic (Lars Mathiassen, 2000,
\np. 73).<\/p>\n

Object structures
\n<\/strong> The relations between objects are – opposite to classes – specific and dynamic, and consists of
\neither an aggregation or an association. An aggregation structure means that one object is a
\nfundamental and defining part of the other (Lars Mathiassen, 2000, p. 77). Aggregations can be
\nexpressed linguistically using the formulation \u201chas-a\u201d (Lars Mathiassen, 2000, p. 78). Likewise
\nthe classes that are aggregated can be linguistically expressed as \u201cpart-of\u201d or \u201cowned-by\u201d (see
\nfigure 4.2).<\/p>\n

An association structure is much like the aggregation structure, but the difference is that the
\nassociated objects are not fundamental and defining for one another. Therefore the association
\nstructure is often used when an aggregation structure would imply a too strong relation
\n(Lars Mathiassen, 2000, p. 79). The association structure can be linguistically expressed as
\n\u201cknows\u201d or \u201cassociated with\u201d.<\/p>\n

When creating the class diagram it is important to numerate the possible relations. If for
\nexample object A is an aggregation of zero or more object B\u2019s, this is denoted by “0..*”
\n(Lars Mathiassen, 2000, p. 78).<\/p>\n

Creating class diagrams
\n<\/strong> When the class diagram is being created it is important to only model the necessary structural
\nrelations (Lars Mathiassen, 2000, p. 86). Likewise the use of generalisations and aggregations should only be applied when they add anything relevant to the description. The names,
\nconcepts, and structural relations should reflect the users\u2019 understanding of the problem domain.
\nBut they do not necessarily have to be completely identical (Lars Mathiassen, 2000, p. 87).
\nThough the best case scenario would be that the problem domain reflects a future user\u2019s
\nunderstanding of the problem domain.
\nThe graphical notation of the relation structures between classes is illustrated in figure 4.2.<\/p>\n


\nFigure 4.2. Graphical notations of structures<\/p>\n

Class Diagram Analysis example
\n<\/strong> In section 4.1.2 we described that our problem domain contains four classes: Employee, Manager,
\nTeam, and Questionnaire. The employee and manager classes could be described as roles for a
\nnew general class user. The validity of this choice is tested using the linguistic formulation for
\naggregations “has-a” and the linguistic formulation for generalisations, “is-a”. So “a user has a
\nrole” and \u201ca manager is a role\u201d. This confirms that these classes can be roles of a class called
\nuser. There are no objects related to Role so this is an abstract class, and the class name is
\ntherefore written in italic in the class diagram.<\/p>\n

The primary job for the manager is to compose new teams. The relation between the manager
\n<\/em> class and the team class could therefore be described as an association. They have a meaningful
\nrelation but one object is not fundamental or defining of the other. This relation is linguistically
\nexpressed as \u201ca manager is associated with a team\u201d. One team can be managed by one or more
\nmanagers, while one manager manages zero or more teams. This is respectively denoted as
\n“1..*” and “0..*” in the class diagram.<\/p>\n

The Team class could be described as an aggregation of employee-objects, because the selected
\nemployees make up a specific team. Without these employees there would not be a team. The
\nvalidity of this choice could be tested by using the linguistic formulation for aggregations, “hasa” or “is-part-of”. So “a team has an employee” and “an employee is part of a team”. One
\nemployee can be part of zero or more teams, while one team requires two or more employees.
\nThe employees fill out questionnaires in order for the managers to collect data about the
\nemployees competences and personality types. For this reason the employee class is associated
\nwith the questionnaire class. There are multiple types of questionnaires based on the employees
\nfields of work. For this reason one employee is associated with one or more questionnaires, and
\none questionnaire is associated with many employees.<\/p>\n

The managers create the questionnaires, which is why the manager class are related to the
\nquestionnaire class. The managers are not a defining property of the questionnaire objects and
\nvice versa. For this reason the relation is an association structure, and not an aggregation
\nstructure. One manager can be associated with zero or more questionnaires, while one questionnaire is associated with at least one manager.
\nThe managers manage the employees which is why they are related. Like the manager and
\nquestionnaire relation, the managers are not a defining property for the employees, which is
\nwhy the relation is an association structure. One manager can manage zero or more employees,
\nand one employee can have zero or more managers.
\nThis results in the class diagram shown in figure 4.3.<\/p>\n


\nFigure 4.3. Class diagram for the problem domain<\/p>\n\n","protected":false},"excerpt":{"rendered":"

Structure After having established the classes in the system, the structure will now be defined with the use of a class diagram. Theory The purpose of the class diagram is to describe structural relations between objects and classes in a problem domain (Lars Mathiassen, 2000, p. 71). The structural relations are different for the classesL\u00e6s mere omClass diagram<\/span>[…]<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":1725,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":[],"yoast_head":"\nClass diagram - HHX opgaver og notater<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/rentabilitet.dk\/opgaver\/diverse-eksamensopgaver\/class-diagram\/\" \/>\n<meta property=\"og:locale\" content=\"da_DK\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Class diagram - HHX opgaver og notater\" \/>\n<meta property=\"og:description\" content=\"Structure After having established the classes in the system, the structure will now be defined with the use of a class diagram. Theory The purpose of the class diagram is to describe structural relations between objects and classes in a problem domain (Lars Mathiassen, 2000, p. 71). 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